Profile frames for windows and doors generally comprise, in the simplest form, respectively four profile rods that have to be welded if plastics material is used. Frequently, however, posts or bars are also used to divide them. Profile frames without posts or bars can be welded to one another without difficulty. This would be possible with posts or bars too, but only above a certain size. To weld the profile rods, a range of devices for welding plastics profiles is known. A distinction is made here between single-head, sequential, four-head, six-head and eight-head machines. When single-head machines are used, each corner connection is welded individually to the profile frame. Sequential machines are constructed with two or more welding heads. Here, the profile frames are welded first on one side and then on the other side. The profile frames with posts can also be made such that first the post connection and then the corner connections are made, with a separate operational step being required for each side. If four-head to eight-head machines are used, the profile frames are typically welded in one operational step. However, it is also possible to make the post connection on other machines; this may be done, for example, by welding the post connection on separate machines. However, it is also known for the post connections to be secured to the frame for example by screws. A further possibility is to make the welded connection or screwed connection of the post between two profile rods first and then, in a final operational procedure, to weld the frame, for example on a four-head welding machine.
The welding machines described above also differ from one another in that different feed processes are used during the joining procedure for the profile rods that are heated up and are to be welded together. For this, two feed processes are known. One is what is called the diagonal feed process, and the other is what is called the parallel feed process. In the diagonal feed process, after heating up at least one profile rod is moved at an angle of 45° in relation to the later welded connection or welding face. In the parallel feed process, the direction of movement is at 90° to the welding faces. The two different processes are determined by the type of construction of the welding machines and the shape of the windows or doors. In principle, the aim is to use the parallel feed process, since better corner strength values of the welded connections can be achieved with it. This is in particular because during joining, in contrast to the diagonal feed process, there is no relative movement along the plane of joining.
During welding of the plastics profile rods, the functional sequence is the following:
The profile rods have to be clamped in the correct position on the beds or carriages with the aid of stop faces on the longitudinal sides and adjustments of the miter faces. Here, the carriages move toward fixed or adjustable stops. During the partial melting and warming up of the welding faces against the heating element, further stops are used. Only when the connection is joined do the carriages move into their end position. Here, a distinction is made between stops for the insertion and welding positions and stops for the joining positions. The different feed processes also result in different carriage positions. The stops are brought into the operational position from their starting position, for example by pneumatic cylinders. The problem of a machine with both feed processes is in this case the large number of stops required for this. Furthermore, the carriages would have to be in different starting positions, and the adjusting parts and heating elements would have to be brought into two different operational positions. For this construction, there is a considerable space requirement in the machine, and in most cases this is not available and additionally gives rise to considerable extra costs.